In the extracorporeal circulation therapy, a hollow-fiber membrane blood purification device using a hollow-fiber membrane as a selective separation membrane has been widely used. A hollow-fiber membrane blood purification device is used, for example, in hemodialysis, which is used as a maintenance therapy for chronic renal failure patients; in hemofiltration and hemodiafiltration, which are used as an acute blood purification therapy and a maintenance therapy for acute and chronic renal failure patients; in continuous hemodialysis, continuous hemofiltration and continuous hemodiafiltration, which are used as an acute blood purification therapy for patients with serious conditions such as acute renal failure and sepsis; and oxygenation to the blood and plasmapheresis during open heart surgery.
Recently, in order to control mechanical strength, chemical stability and permeability, a selective separation membrane made of a polysulfone resin or a cellulose acetate resin has been spread at a high speed. Since the polysulfone resin and cellulose acetate resin are hydrophobic polymers, a selective separation membrane consisting of the polysulfone resin or cellulose acetate resin alone is extremely insufficient in hydrophilicity of the membrane surface. Because of this, the selective separation membrane has drawbacks in that blood compatibility is low; the membrane interacts with blood components, easily causing blood coagulation; and protein components absorb to the membrane, easily decreasing permeability.
To make up for these drawbacks, attempts have been made to provide a selective separation membrane with blood compatibility by using a hydrophilic polymer, such as polyvinylpyrrolidone (PVP), polyvinyl alcohol and polyethylene glycol, in a selective separation membrane, in addition to a hydrophobic polymer. For example, a method of improving blood compatibility by enhancing hydrophilicity of the membrane by producing a membrane from a spinning dope for membrane production containing a hydrophobic polymer and a hydrophilic polymer blended together; and a method of providing blood compatibility by coating the membrane with the hydrophilic polymer, in a dry-wet membrane production step, for example, by producing a membrane using a hollow-portion internal liquid containing a hydrophilic polymer, followed by drying; or by bringing the produced membrane into contact with a solution containing a hydrophilic polymer, followed by drying, are known.
In addition, recently, in order to mitigate oxidative stress markedly observed in long-term dialysis patients, a dialyzer provided with a lipid-soluble substance having antioxidative property has been developed. For example, an attempt to remove a causative substance of oxidative stress, i.e., a peroxide, by using a hollow-fiber membrane and an attempt to recover an antioxidative effect of a living body, have been made.
Patent Literatures 1 and 2 disclose a blood purification device containing a lipid-soluble vitamin such as vitamin E having various physiological actions such as in-vivo antioxidative action, biomembrane stabilizing action and platelet-aggregation suppressive action. It is known that one of the hydrophobic polymers, a polysulfone resin, has high affinity for a lipid-soluble vitamin, which is effective for suppressing oxidative stress induced by extracorporeal blood circulation; and that a lipid-soluble vitamin is easily immobilized to the surface of a hollow-fiber membrane.
Since a blood purification device is medical equipment, sterilization is required. As a sterilization method, radiation sterilization using e.g., γ ray and an electron beam has been mainly used. A hollow-fiber membrane blood purification device sterilized with a radial ray has a problem in that a lipid-soluble substance is e.g., decomposed and degraded by a peroxide substance produced by sterilization, with the result that antioxidative property and blood compatibility decrease.
As a method for preventing performance deterioration of a hollow-fiber membrane, Patent Literatures 3 and 4 disclose a method for preventing oxidative degradation of a hollow-fiber membrane due to sterilization by controlling the oxygen concentration within a hollow-fiber membrane blood purification device and the moisture content of the hollow-fiber membrane during sterilization.